Re: Just Normlicht vs. Graphiclite or GTI
Re: Just Normlicht vs. Graphiclite or GTI
- Subject: Re: Just Normlicht vs. Graphiclite or GTI
- From: Johannes Hoffstadt <email@hidden>
- Date: Fri, 06 May 2005 12:34:56 +0200
Hi all, one thing to keep in mind is that CRI does not compare to D50.
CIE publication 13.3 describes the exact procedure. Depending on the
correlated color temperature (CCT) of the test light source, CRI is
calculated with reference to < 5000 K : a Planckian radiator with the
same CCT >= 5000 K : a CIE Dxxxx daylight with the same CCT That's why
CIE standard illuminant A has an CRI of 100, and CIE standard illuminant
D65 also has an CRI of 100. It also means that CRI alone is not
necessarily a good indicator of the quality of D50 simulation in
particular. (ISO 3664:2000 combines chromaticity, CRI, and MI to get a
good hold on the quality of daylight booths.) Another point to be made
is that you are required to do these calculations based on illuminant
spectra with 5 nm intervals or smaller. I don't know yet how big the
impact of 10 nm intervals on the accuracy can be - but I guess that 5
CRI units difference are possible (if you take into account that CRI is
sort of a Delta E (well, 64) scaled by 4.6, then an error of just 1
Delta E already makes 4.6 CRI units difference). Has anybody here had
the chance to do some comparisons? As a side note, jagged spectra do not
come with a lower quality by default - I'd say it very much depends on
where the spikes are... Best regards, Hanno --- Dr. Johannes Hoffstadt
Color Solutions Software www.basiccolor.de Steve Jenkins wrote:
Steve, Yes, I agree this is confusing... My only point is that if you
load these spectra into i1Share you'll see why Mr. Holm's original
observation is difficult to understand/comprehend... According to
i1Share: JUST lamps = 96 CRI GTI lamps = 90 CRI BUT if you look at the
spectral distribution of the JUSTs they look more jagged... I'm still
not sure what to make of all this... Thanks, Steve Jenkins -----
Original Message ----- From: "Steve Upton" <email@hidden> To:
<email@hidden> Sent: Thursday, May 05, 2005 07:23
PM Subject: Re: Just Normlicht vs. Graphiclite or GTI
At 7:06 PM -0400 5/5/05, stevej wrote:
>Steve,
>
>Thanks for your quick response but please don't put
>words in my mouth. I don't remember implying anything
>about which one was "correct". In fact my last words were
>"go figure". All I was trying to show is why this happens.
>Please reread my original message.
sorry about that... not meaning to put words in anyone's mouth, just wanting to clear up possible confusion.
when you wrote
>"> >Since RHEM strips are especially susceptible to red metamerism
>> >and the JUST tubes have a sharp drop beyond 650nm, you've
>> >got metamerism even though the JUST lights DO have a
>> >higher CRI. Go figure..."
I took the "you've got metamerism even though...higher CRI" as a direct comparison between Just and GTI illuminants but I find the logic unclear - the metamerism is between Just and GTI but CRI is between Just and D50?
does this (my confusion) make sense?
I'm still curious about how each compares to D50...
Regards,
Steve
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